There is substantial debate about the influence of various environmental factors on IQ test score differences between races and ethnic groups in a given country, and whether or not genetics may also play a role.[1]

Contents

Measuring intelligence

Several different ways of measuring intelligence have been proposed. IQ tests are the most common and what is usually used in research. The American Psychological Association (APA) states in its 1997 report Intelligence: Knowns and Unknowns that "the dominant psychometric approach, which has not only inspired the most research and attracted the most attention (up to this time) but is by far the most widely used in practical settings...The psychometric approach is the oldest and best established, but others also have much to contribute. We should be open to the possibility that our understanding of intelligence in the future will be rather different from what it is today."'[2]

Christine E. Daley, Anthony J. Onwuegbuzie, Howard Gardner and other psychologists have challenged the classicist model of a single index for "intelligence" on which hereditarian assumptions of racial disparity are based. They advocate a theory of multiple intelligences. They write that through research on multiple intelligences they may reveal a more nuanced perspective in to the strengths and weaknesses of students and in to the ways that people view the intelligences of people from other ethnic groups. [3]Cultural differences may lead children to develop different strengths in different areas of intelligence. Leroy G. Baruth and M. Lee Manning write "Knowing that a relationship exists between cultures and education is a prerequisite to effective teaching, but continuing to teach with styles and strategies appropriate only for middle-class Anglo learners fails to meet the needs of culturally diverse children and adolescents." [4].

Ketty M. Sarouphim writes in Discovering Multiple Intelligences through a Performance-Based Assessment: Consistency with Independent Ratings[5] that the use of standardized tests to assess the intelligence of culturally diverse groups has been much criticized [6]. Some researchers have attributed the problem of underrepresentation of minority students in programs for the gifted to the wide use of such tests in which narrow definitions of giftedness are adopted [7]. Sarouphim writes that the field of intelligence assessment seems to be witnessing a paradigm shift, as evidenced by recent definitions of giftedness[8], the emergence of nontraditional theories of intelligence[9], and the rise of alternative assessment methods, namely performance-based assessments[10].

Facial recognition ability has shown differences by race.[11] In general, other-race faces are less accurately recognized than same race faces but classified faster by race.[12] In the US Blacks' performance is significantly better than that of whites', and blacks are better at recognizing faces of whites than whites are at recognizing blacks.[13][14] Richard Ferraro writes that facial recognition is an example of a neuropsychological measure that can be used to assess cognitive abilities that are salient within African-American culture.[15] One possibility is that expertise in perceiving faces of particular races is associated with increased ability to extract information about the spatial relationships between different features.[16]

Test bias

While the existence of average IQ test score differences has been a matter of accepted fact for decades, during the 1960s and 1970s a great deal of controversy existed among scholars over the question of whether these score differences reflected real differences in cognitive ability. Some claim that there is no evidence for test bias since IQ tests are equally good predictors of IQ-related factors (such as school performance) for U.S. Blacks and Whites.[17] The performance differences persist in tests and testing situations in which care has been taken to eliminate bias.[17] It has also been suggested that IQ tests are formulated in such a way as to disadvantage minorities.[17] Controlled studies have shown that test construction does not substantially contribute to the IQ gap.[17] Still, a 2007 study at Case Western Reserve University found that cultural differences in the provision of information account for racial differences in IQ. The study also found that test problems, similar to some problems found on conventional IQ tests, were only solvable on the basis of specific previous knowledge. Such specific knowledge based questions showed evidence of test bias since the performance on non-specific knowledge based questions did not always correlate with the performance on the knowledge based question.[18]

On a test (Black Intelligence Test of Cultural Homogeneity) oriented toward the language, attitudes, and life-styles of Afro-Americans, white students perform more poorly than blacks do on tests oriented toward white middle-class values, indicating that there are important dissimilarities in the cultural backgrounds of blacks and whites.[19] Some argue that these findings indicate that test bias plays a role in producing the gaps in intelligence test scores.[20]The Chitling Intelligence Test is another example of a culturally biased test that tends to favor African Americans.[21] These criticisms may not apply to "culture free" tests of intelligence. However, due to their cultural backgrounds some test takers do not have the familiarity with the language and culture of the psychological and educational tests that is implicitly assumed in the assessment procedure, even on "culture free" tests.[22]

Environmental explanations

Regarding the IQ gaps in the U.S., numerous explanations beside genetics have been proposed. Joel Wiesen lists more than a hundred.[23] It has been suggested by John Ogbu and others that African-American culture disfavors academic achievement and fosters an environment that is damaging to IQ.[24] Likewise, it is argued that the persistence of negative racial stereotypes reinforces this effect. Ogbu writes that the condition of being a "caste-like minority" affects motivation and achievement, depressing IQ.[25][26] Although cultural differences may play a role in creating the gaps, much of the present gap found in IQ tests scores is likely the result of a combination of socioeconomic factors and health factors, such a breastfeeding. A 2006 study found that strongest and most robust predictors of intelligence were family income, parental education and breast feeding, with these three variables explaining 7.5% of the variation in intelligence at age 14.[27] The impact of racial stereotypes has also been shown to play a key role. Making race salient in testing stations depresses the performance of minority students who belong to racial groups that have been historically stereotyped as less intelligent. (See:Race and intelligence (media portrayal)) Recent developments in intervention methods to counteract the impact of negative stereotypes have proved promising.

Arguing that IQ tests are often wrongly described as measuring "innate" rather than developed ability, Jencks and Phillips 1998 write that this "labeling bias" causes people to inappropriately attribute the Black-White gap to "innate" differences.[28]
They argue that non-cultural environmental factors cause gaps measured by the tests, rather than innate difference based on genetics, and that to use these tests as a measure of innate difference is misleading and improper.[29]

Increases in IQ scores over time

William T. Dickens and James R. Flynn write that blacks have gained 5 or 6 IQ points on non-Hispanic whites between 1972 and 2002. This graph shows the gains for various tests.[30]

The secular, international increase in test scores, commonly called the Flynn effect, is seen by Flynn and others as reason to expect the eventual convergence of average black and white IQ scores. Flynn argues that the average IQ scores in several countries have increased about 3 points per decade during the 20th century, which he and others attribute predominantly to environmental causes.[31] This means, given the same test, the mean black American performance today could be higher than the mean white American performance in 1920, though the gains causing this appear to have occurred predominantly in the lower half of the IQ distribution.[32] If changes in environment can cause changes in IQ over time, they argue, then contemporary differences between groups could also be due to an unknown environmental factor. On the supposition that the effect started earlier for whites, because their social and economical conditions began to improve earlier than did those of blacks, they anticipate that the IQ gap among races might change in the future or is even now changing. An added complication to this hypothesis is the question of whether the secular IQ gains can be predominantly a real change in cognitive ability. Flynn's face-value answer to this question is "No",[33] and other researchers have found reason to concur. Wicherts et al. 2004 wrote that "the gains cannot be explained solely by increases at the level of the latent variables (common factors), which IQ tests purport to measure". An analysis by Rushton 1999 reported that the IQ increases associated with the Flynn effect did not produce changes in g, which Rushton compares to the finding by Jensen 1998a that IQ increases associated with adoption likewise do not increase g. Flynn 1999b disagrees with Rushton's analysis.

Dickens and Flynn 2001 have proposed a solution which rests on genotype-environment correlation, hypothesizing that small initial differences in environment cause feedback effects which magnify into large IQ differences. Rowe and Rodgers 2002 and others find this hypothesis unsupported by the available evidence. Dickens and Flynn 2002 respond to these criticisms. Such differences would need to develop before age 3, when the black-white IQ gap can be first detected.[34]

The Flynn effect consists of large documented worldwide increases in IQ scores for at least several decades. Attempted explanations have included improved nutrition, a trend towards smaller families, better education, greater environmental complexity, and heterosis.

Comparing the Flynn effect (IQ differences within races over time) to contemporary IQ differences between races is contested; for example, one report concludes "the nature of the Flynn effect is qualitatively different from the nature of black-white differences in the United States," and that "the implications of the Flynn effect for black-white differences appear small" However, this refers to "measurement invariance", is not a statement about the role of genetics in the B-W gap, and is a relatively minor statement that not mentioned in the abstract.(Wicherts et al. 2004).

A recent theory hypothesizes that fluid cognition (gF') may be separable from general intelligence, and that gF' may be very susceptible to environmental factors, in particular early childhood stress. Some IQ tests, especially those used with children, are poor measures of gF', which means that the effect of the environment on intelligence regarding racial differences, the Flynn effect, early childhood intervention, and life outcomes may have been underestimated in many studies. The article has received numerous peer commentaries for and against.[35]

A recent, newly available, large, and nationally representative data set find only very small (0.06 SD between whites and blacks) racial differences on measures for mental function for children aged eight to twelve months. These differences disappear when controlling for a limited set of factors such as differences in SES. "These findings pose a substantial challenge to the simplest, most direct, and most often articulated genetic stories regarding racial differences in mental function." "To the extent that there are any genetically-driven racial differences in intelligence, these gaps must either emerge after the age of one, or operate along dimensions not captured by this early test of mental cognition."[36]In their 2006 study, Black Americans reduce the racial IQ gap: Evidence from standardization samples, William T. Dickens and James R. Flynn write that blacks have gained 5 or 6 IQ points on non-Hispanic whites between 1972 and 2002. Gains have been fairly uniform across the entire range of black cognitive ability.[37]

The collection of ethnic and racial statistics has become common in a growing number of institutional settings. Yet contemporary approaches to race and ethnicity suggest that the very process of compelling people to assign themselves to one of a small number of racial or ethnic 'boxes' is, at best, essentialist and, at worst, racist.[39]

Stereotype threat

An experiment on college students in 1995 showed the impact of Stereotype threat by asking students to fill out a form before taking the test indicating their race. The scores in this graph have been adjusted by SAT.[40]

Stereotype threat is the fear that one's behavior will confirm an existing stereotype of a group with which one identifies. This fear may in turn lead to an impairment of performance (Aronson, Wilson, & Akert, 2005). Stereotype threat has been documented by the social psychologists Claude Steele, Joshua Aronson, Irwin Katz, and Steven Spencer, who have conducted several studies on this topic.

Steele and Aronson write that making race salient when taking a test of cognitive ability negatively affected high-ability African American students.[41] Steele writes that the stigma of being African American is still relevant, as it has an effect on the educational outcomes of African Americans. Stereotypes such as: Asian-Americans excelling in mathematics or African-Americans always testing poorly can be extremely harmful. Stereotype threats can seriously alter academic achievement and motivation.[42]

In a paper prepared for an APA convention, Steele writes: "Thus the predicament of 'stereotype vulnerability': The group members then know that anything about them or anything they do that fits the stereotype can be taken as confirming it as self-characteristic, in the eyes of others, and perhaps even in their own eyes. This vulnerability amounts to a jeopardy of double devaluation: once for whatever bad thing the stereotype-fitting behavior or feature would say about anyone, and again for its confirmation of the bad things alleged in the stereotype."

Steele and Aronson are not first to test stereotype threat. During the 1960’s Irwin Katz, psychologist, suggested that stereotype threat could also influence performance on IQ tests. Katz found that Blacks were able to score better an IQ subtest if the test was presented as a test of eye-hand coordination. Blacks also scored higher on an IQ test when they believe the test will be compared to that of other blacks.[43] Katz concluded that his subjects were thoroughly aware of the judgment of intellectual inferiority held by many white Americans. With little expectation of overruling this judgment, their motivation was low, and so were their scores.[44] Paul Sackett, a psychologist agrees that stereotype threat is a real phenomenon and that it is is a potentially important contributor to the racial achievement gap. He cautions however, that these findings may be widely misinterpreted to mean that eliminating stereotype threat eliminates the entire Black-White performance gap, and encourages researchers to continue their study of this and other phenomena. [45]

Since stereotype threat appears to be one key contributing factors to the gaps in test scores, researchers Geoffrey L. Cohen, Julio Garcia, Nancy Apfel, and Allison Master proposed intervention methods to address the problem in 2006. The intervention, a brief in-class writing assignment, significantly improved the grades of African American students and reduced the racial achievement gap by 40%. These results suggest that the racial achievement gap, a major social concern in the United States, could be ameliorated by the use of timely and targeted social-psychological interventions.[46]

Physiological responses to racism

Stereotype threat can result in physiological responses that can be measured objectively. For example, a study by Blascovich J, Spencer SJ, Quinn D and Steele C. reported that African Americans under stereotype threat exhibited larger increases in arterial blood pressure during an academic test, and performed more poorly on difficult test items. Some researchers feel this may explain the higher death rates from hypertension related disorders among African Americans.[47]

A study by Toni Schmader and Michael Johns reported that stereotype threat can effectively reduce working memory capacity, another factor in poor test performance.[48]

Caste-like minorities

John Uzo Ogbu Anthropologist known for his theories on "caste-like minorities" and "The effort gap"

John Ogbu writes that caste-like minorities are not the same as other racial minorities. Caste-like minorities are incorporated into a country involuntarily and permanently. These include Blacks, American Indians, Mexicans, Native Hawaiians, Puerto Ricans and others. Membership is a low caste acquired at birth and retained permanently. Caste members are regarded by the white majority as inferior and not desirable as neighbors or workmates. Often, they lack political power and are economically subordinate. They face a job ceiling, and are not hired on the basis of training and skills like other minorities. Caste-like groups also reject the ideology and beliefs of the dominant group culture. They believe their problems are due to the "system" and racism than their own inadequacies. They may develop a "collective institutional discrimination perspective". This leads them into channel efforts into collective struggle.[50]

Like Blacks and Hispanics in the U.S., minorities in non-US societies show achievement gaps (such as the Māori in New Zealand, aboriginals in Australia, scheduled castes ("untouchables") in India, non-European Jews in Israel, and the Burakumin in Japan). The most prominent finding cited is that Northern Irish Catholics used to score about 15 points lower than Protestants. Similarly, Irish, Italian and Polish immigrants in the U.S. are reported to have all scored about 80 in the beginning of the 19th century, but now tend to reach 100. The same is true of persons from rural versus urban areas in general (see e.g., this article by conservative columnist and economist Thomas Sowell and this page on European and Greek IQ. More arguments of the kind are to be found here).

Quality of education

Some researches have written that studies that find test performance gaps between races even after adjusting for education level, such as the analysis found in The Bell Curve, fail to adjust for the quality of education. Not all high school graduates or college graduates have received the same quality of education. A 2006 study reported that that years of education is an inadequate measure of the educational experience among multicultural elders, and that adjusting for quality of education greatly reduced the overall effect of racial differences on the tests.[51] A 2004 study reported that quality of education and cultural experience influence how older African Americans approach neuropsychological tasks and concluded that adjustment for these variables may improve specificity of neuropsychological measures.[52][verification needed] Yet another study reported that, although significant differences were observed between the ethnic groups when matched for years of education, equating for literacy level eliminated all performance differences between African Americans and Whites on both cancellation tasks which assess visual scanning.[53][verification needed] (Like reaction time tests cancellation task tests are sometimes regarded as "culture free" tests of intelligence.) Eric A. Hanushek and Steven G. Rivkin wrote in their 2006 book that unequal distributions of inexperienced teachers and of racial concentrations in schools can explain all of the increased achievement gap between grades 3 and 8.[54]

A 2004 study in South Africa found highly significant effects for both level and quality of education within the black African first language groups taking the Wechsler IQ tests. Scores black African first language groups with advantaged education were comparable with the US standardization, whereas scores for black African first language participants with disadvantaged education were significantly lower than this. The study cautioned that faulty conclusions may be drawn about the effects of ethnicity and the potential for neuropsychologicalmisdiagnosis.[55]

Racial discrimination in education

Roslyn Arlin Mickelson writes that racial discrimination in education arises from actions of institutions or individual state actors, their attitudes and ideologies, or processes that systematically treat students from different racial/ethnic groups disparately or inequitably.[56] Despite advancement in education reform efforts, to this day African American students continue to experience inequities within the educational system. Hala Elhoweris , Kagendo Mutua , Negmeldin Alsheikh and Pauline Holloway conducted a study of the effect of students' ethnicity on teachers' educational decision making. The results of this study indicated that the student's ethnicity did make a difference in the teachers' referral decisions for gifted and talented educational programs.[57]Recently, a number of scholars have examined the issue of disproportionate representation of minority students in special education programs [58][59]

Teachers' perceptions of a students cultural background may effect school achievement. African American students with African American cultural backgrounds, for example, have been found to benefit from culturally responsive teaching.[60] In a 2003 study researchers found that teachers perceived students with African American culture-related movement styles as lower in achievement, higher in aggression, and more likely to need special education services than students with standard movement styles irrespective of race or other academic indicators. [61]

Ellis Cose writes that low expectations may have a negative impact on the achievement of minorities. He writes that black people did not need to read The Bell Curve to be aware of the low expectations held for them by the majority culture. He recalls examples of low expectations from his teachers in school who regarded his use of AAVE as "laziness" and teachers who did not feel it was important to purchase new text books because they did not expect the students to be able to read anything complex. He contrasts these low expectations with the high expectations philosophy of Xavier University where, using the ideas Whimbey articulated in his book Intelligence can be Taught teachers created a program called SOAR. SOAR raised the performance of black students and lead Xavier to become the university that sends the greatest number of black students to medical school in the United States. The SOAR program produced gains equivalent to 120 points on an SAT test. Cose writes that "..we must treat people, whatever their color, as if they have unlimited intellectual capacity."[62]

Socio-economic factors

Min-Hsiung Huang and Robert M. Hauser found that, controlling for social background, the Black-White test score gap narrowed significantly over the period from 1974 to 1998. For Whites, however, improvement in social background across time does not raise test scores correspondingly. [63]

According to a 1995 report released by the American Psychological Association, the black-white score gap "is not eliminated when groups or individuals are matched for SES". The report concludes that no "simple income- and education-based index can adequately describe the situation of African Americans though, it is clear, they say, that these differences, are well within the range of effect sizes that can be produced by environmental factors".[64]

IQ is correlated with economic factors. Blacks and Hispanics suffer poorer economic conditions than Whites. It has been suggested that the effects of poverty are responsible for some or all of the IQ gap. However, in the American Psychological Association report Neisser et al. (1996) argue that economics cannot be the whole explanation. According to Richard J. Herrnstein and Charles Murray, authors of The Bell Curve, to the moderate extent that IQ and income are related, it appears that IQ determines income, and not the other way around (Murray 1998). There are, however, many other potential Socio-economic factors factors beside income.

Researchers have reported that many American Blacks and Hispanics are not given sufficient opportunity to learn language and thinking skills during the first three years of life, possibly due to economic status. The first three years are especially critical years for neural development of the brain, and previous studies have shown that when human children were deprived of most or all language skills at an early age, they never developed the ability to master language at a later age; if they only mastered a small amount of language and thinking skills at a young age, then they could only make small improvements in later years. A recent study has shown that many American Blacks and Hispanics are raised in homes where their parents speak relatively few sentences, and the sentences usually show only simple grammar. As a result, their children never hear millions of words during the time when their brains are developing linguistic skills. Without this linguistic input during their developing years, many are observed to quickly fall behind, and they can never catch up. Children in poorer welfare families, which includes a higher percentage of many minority populations, apparently hear up to 30 million fewer words by age three than children in higher income, usually White, families. (Source: The Early Catastrophe: The 30 Million Word Gap by Age 3)

Work by Carneiro et al. (2005) on average Black-Hispanic-White differences in IQ, education, and income casts doubt on conventional explanations of Black-White differences:

Hispanic children start with cognitive and noncognitive deficits similar to those of black children. They also grow up in similarly disadvantaged environments and are likely to attend schools of similar quality. Hispanics complete much less schooling than blacks. Nevertheless, the ability growth by years of schooling is much higher for Hispanics than for blacks. By the time they reach adulthood, Hispanics have significantly higher test scores than do blacks. Conditional on test scores, there is no evidence of an important Hispanic-white wage gap. Our analysis of the Hispanic data illuminates the traditional study of black-white differences and casts doubt on many conventional explanations of these differences because they do not apply to Hispanics, who also suffer from many of the same disadvantages. The failure of the Hispanic-white gap to widen with schooling or age casts doubt on the claim that poor schools and bad neighborhoods are the reasons for the slow growth rate of black test scores.

A recent 1996 study using multiple socio-economic factors have accounted for 80% of the gap, and suggest that any remaining gap is statistically insignificant.[65]

Health

Percentage of children aged 1-5 with blood lead levels at least 10 µg/dL. Black and hispanic children have much higher levels than white children. A 10 µg/dL increase in blood lead at 24 months is associated with a 5.8-point decline in IQ.[66] In 1976 77.8% of all children had at least this much lead in their blood.[67]

In the developing world there are are many factors can greatly decrease IQ scores. Examples include nutrition deficiencies in iodine and iron; certain diseases like malaria; unregulated toxic industrial substances like lead and mercury; and poor health care for pregnant women and infants. Also in the developed world there are many biological factors that can affect IQ. Increased rates of low birth weight babies and lower rates of breastfeeding in Blacks as compared to Whites are some factors of many that have been proposed to affect the IQ gap.[68]

Other researchers have come across what they see as additional reasons for the IQ gap. The paper Poverty and Brain Development in Early Childhood holds that there is a large amount of neural damage in many American Black and Hispanic children due to inadequate nutrition, substance abuse of the children's parents, a high incidence of maternal depression, exposure to environmental toxins, psychological trauma, and the neural effects of physical abuse. Masters (1997) has proposed a "neurotoxity hypothesis" where pre- and post-natal exposure to heavy metal poisons differentially impacts Blacks. Black children have much higher lead levels than white children.[69]Drug abuse during pregnancy (e.g., alcohol and phenobarbital) can negatively affect IQ.

Infant mortality may be an indicator of environmental conditions that are sublethal but damaging to health. The rate of infant mortality in the U.S. Black population is twice that of the White population, which in turn is twice the rate of infant mortality among Asians.[70] The rates of low birth weight (LBW), defined as less than 5.5 pounds, are correlated with infant death. LBW is different than premature birth; LBW can occur in full-term babies. LBW babies are at risk for many developmental, behavioral and cognitive abnormalities, including mental retardation. LBW (and premature birth) affect Blacks at twice the overall rate for the U.S. population.[71] Mother's age is the strongest predictor of LBW, where teenagers are especially susceptible. Most of the Black-White differences in LBW are not account for by other environmental variables such as socioeconomic status, poverty status, mother's age, and education; but differential prenatal care explains some of the gap (Naylor and Myrianthopoulos 1967). Thus, the cause of the Black-White gap in LBW is a mystery. Environmental intervention has strong but short-lasting effects on IQ among LBW babies (Brooks-Gunn et al. 1994). Studies of LBW Black and White babies matched for birth weight and gestational age still find a one standard deviation IQ gap (Montie and Fagan 1998).

A study of LBW babies indicates that breastfeeding can significantly improve their IQ scores tested at 8 years old (Lucas et al. 1996). After controlling for possible confounding factors, an improvement of 8.3 IQ points was reported in the breastfed group as compared to the formula fed group. Black mothers are known to breastfeed infants less and for a shorter time than White mothers (Ryan et al. 1996; Leary 1988)[72]Studies have shown IQ gains lasting into adulthood with increased duration of breastfeeding. Several recent studies shows that the intake of certain micronutrients, like those present in breast milk or fish oil, affects IQ scores even in developed nations. Helland et al (2003) have shown larger head size at birth and higher IQ scores at 4 years of age when mothers took fish oil supplements during pregnancy and lactation.[73]Jensen (1998) believes that dietary supplementation is a promising avenue of research for raising Black children's levels of g. Lynn (1990) has proposed a nutritional hypothesis for the Flynn effect.

Exposure to violence in childhood has been associated with lower school grades[74] and lower IQ in children of all races.[75] A group of largely African American urban first-grade children and their caregivers were evaluated using self-report, interview, and standardized tests, including IQ tests. The study reported that exposure to violence and trauma-related distress in young children were associated with substantial decrements in IQ and reading achievement. Exposure to Violence or Trauma lead to a 7.5-point (SD, 0.5) decrement in IQ and a 9.8-point (SD, 0.66) decrement in reading achievement.[74] Violence may have a negative impact on IQ, or IQ may be protective against violence.[75] The causal mechanism and direction of causation is unknown.[74] Neighborhood risk has been related to lower school grades for African-American adolescents in another study from 2006.[76]

Culture

Many anthropologists[attribution needed] have argued that intelligence is a cultural category; some cultures emphasize speed and competition more than others, for example. Speculations about innate differences in intelligence between ethnic groups have occurred throughout history. Aristotle in the 4th century B.C. and Cicero in the 1st. century B.C. disparaged the intelligence of the northern Europeans of the time, as did the Moors in Iberia in the 11th century.[77]

Ogbu elaborates on this idea suggesting that African American popular culture serves to disengage students from academic achievement by proving the wrong kind of role models.

"What amazed me is that these kids who come from homes of doctors and lawyers are not thinking like their parents; they don't know how their parents made it," Professor Ogbu said in an interview. "They are looking at rappers in ghettos as their role models, they are looking at entertainers. The parents work two jobs, three jobs, to give their children everything, but they are not guiding their children."[78]

Many anthropologists have argued that intelligence is a cultural category; some cultures emphasize speed and competition more than others, for example. During WWI African-Americans from the north tested higher than those from the south. This could be because African-Americans in the north had received more formal education (see Race: Science and Politics, written by Ruth Benedict in 1940). Thousands of ethnographic studies indicate that innate capacities for cultural evolution are equal among all human populations. The American Anthropological Association has endorsed a statement deriding all studies of race and intelligence .

It's been a personal challenge for Dylan Pritchett, a Lafayette High School senior in Williamsburg who will head to Old Dominion University in August. Friends accused him of not "acting black" when he signed up for AP courses.[79]

Speculations about innate differences in intelligence between ethnic groups have occurred throughout history. Aristotle in the 4th century B.C. and Cicero in the 1rst. century B.C. disparaged the intelligence of the northern Europeans of the time, as did the Moors in Iberia in the 11th century.[80]

It has been suggested that Black culture disfavors academic achievement and fosters an environment that is damaging to IQ (Boykin 1994). Likewise, it is argued that a persistence of racism reinforces this negative effect. John Ogbu[81] has developed a hypothesis that the condition of being a "caste-like minority" affects motivation and achievement, depressing IQ. However, Arthur Jensen has criticized these arguments on the grounds that they cannot explain the higher scores of East Indians and East Asians.[82] Even proponents of the view that the IQ gap is caused partly by genetic differences, such as Arthur Jensen, recognize that non-genetic factors are likely involved. Indeed, one author has compiled a list of over one hundred possible causes of the Black-White IQ gap.[83]

Cultural explanations for the IQ deficit among Blacks and Hispanics compared to Whites and East Asian minorities are complemented – and sometimes challenged – by the observation that East Asian minorities score well on IQ tests and on average enjoy greater economic success than other minorities. Along these lines, East Asians are sometimes referred to as "model minorities". East Asian and Jewish populations have suffered past discrimination and persecution which some argue is evidence against the importance of discrimination for IQ differences.[84] While the severe discrimination against Jews and East Asians have today diminished, many argue that discrimination continue against blacks and that this is impacting the IQ scores of Blacks.

Pidgin language barriers

Sandra Lee McKay author of Sociolinguistics and Language Teaching writes that language may present a barrier for students who speak pidgin and creole languages. Unlike other languages such as Spanish and Chinesepidgin and creole languages such as African American Vernacular English (AAVE) are not commonly recognized in classroom settings. As a result of this, students are not taught the Standard American English (SAE) used on tests as a second language in the same way as students who speak Spanish or Chinese. Students who speak AAVE face challenges similar to those learning English as a Second Language. (ESL)[85]

John Russel Rickford author of Unequal partnership: Sociolinguistics and the African American speech community[86] rebutts misconceptions about the cognitive limitations of the use of AAVE notes the unfair disadvantages IQ tests pose for its speakers. Geneva Smitherman writes that "80 to 90 percent of American blacks” speak AAVE “at least some of the time".[87] Anne H. Charity, Hollis S. Scarborough, Darion M. Griffin found in a 2004 study that higher familiarity with SE was associated with better reading achievement for urban African American students in kindergarten through second grade. The improvement in reading ability was independent of other cognitive measures suggesting that speakers of AAVE face barriers in education.[88] The preponderance of code-switching indicates that AAVE and SAE are met with different reactions or discernments. AAVE is often perceived by members of mainstream American society as indicative of low intelligence or limited education.[89]

Positive language effects

Some argue that the higher IQ test scores in East Asian nations are in part attributed to some IQ tests' inherent bias towards testing spatial reasoning.[How to reference and link to summary or text] They argue that logographic writing systems, like those used by Chinese and Japanese, develop spatial reasoning better than the alphabetic writing systems prevalent in Europe and America, though there are no studies that support this hypothesis. The same reasoning has been used to explain why students from some Asian countries (e.g., Singapore) tend to score better than average in tests of mathematics. Some argue that the East Asian advantage can also be explained by more rigorous education programs. [How to reference and link to summary or text] However, even though few native-born Asian Americans learn to read and write Chinese characters, their performance is above-average on IQ tests.

A direct comparative test between Greek and Chinese students showed no difference in IQ or g, contradicting earlier studies which do not take the finer architecture of mental processing into account. The Chinese did outperform the Greeks in visuo/spatial ability, but this difference was smaller at earlier ages, grew during the first years of schooling and decreased later. The authors suggest that this pattern can be explained as follows: the Chinese students train their visuo/spatial ability during their early school years, as they have to learn many characters of the Chinese writing system. Later in life, the Greek students adopt compensating strategies to deal with visuo/spatial information, and therefore the difference decreases in this realm.[90]

Role-model effects

Thomas S. Dee, in his studyTeachers, Race, and Student Achievement in a Randomized Experiment found that the race of the teacher has impacts on student achievement. An own-race teacher significantly increased the math and reading achievement of both black and white students.[91] Using single-equation regression models Mark O. Evans has also found evidence of effects for African-American students. [92] These findings may confirm the suggestion for the aggressive recruitment of minority teachers are based on hypothesized role-model effects for minority students.

In Sabrina Zirkel's longitudinal study of young adolescents students who reported having at least one race- and gender-matched role model performed better academically up to 24 months later, reported more achievement-oriented goals, enjoyed achievement-relevant activities to a greater degree, thought more about their futures, and looked up to adults rather than peers more often than did students without a race- and gender-matched role model. These effects held only for race- and gender-matched role models—not for non-matched role models.[93]

The effort gap

Researchers Stephan Thernstrom and John Ogbu have suggested that black students perform poorly in part due to simple lack of effort. Stephan Thernstrom studied different kinds of schools and concluded that, while many environmental factors play a role in the achievement gap, a strong commitment to education was an essential element for academic success. Ogbu wrote that the black students were quite open in telling the researchers that, in general, their white classmates studied more, worked harder and cared more about getting good grades.

"In spite of the fact that the students knew and asserted that one had to work hard to succeed in Shaker schools, black students did not generally work hard. In fact, most appeared to be characterized by the low-effort syndrome ... (They) were not highly engaged in their schoolwork and homework." --John Ogbu[94]

Freeman A. Hrabowski III, president of the University of Maryland, Baltimore County, said that many black boys grow up with few male role models and in high-crime neighborhoods, where being smart in school is not considered cool. “You can’t just ignore the needs of a group and say all children are the same,” he said.[95]

Arguments against environmental explanations

Although, researchers such as Jensen, who argue that genetics play a significant role in do acknowledge that environmental factors are important. They have raised a number of questions about various environmental explanations since if any one environmental explanation or any combination of environmental explanations accounted for the entire gap in test scores, the question of a genetic contribution would no longer be relevant. According to Jensen 1998b, "the total between-populations variance accounted for by empirically demonstrable environmental factors does not exceed 20 to 30 percent." Jensen argues that attributing between population difference to factors that have not been shown to affect differences within populations is "useless from the standpoint of scientific explanation". Further, Jensen 1998b writes that many environment-IQ correlations which have been reported, though real and significant, can be disqualified because these studies completely confound the genetic and environmental causes of IQ variance, and in those cases where genetic and environmental causes have been examined, nearly all of the correlations have been found to actually have a genetic basis.

According to Arthur Jensen, we know hardly anything about the magnitude and psychometric properties of test score gaps among "caste-like" minorities in Indian and Japan, but a Black-White gap can be found in places where blacks have never been slaves, where they have never been a minority population, and where there has never been a color line.[96] In response to Sowell, Jensen writes that the poor performance of recent immigrants is usually attributed to deficiencies in English language skills, but that those groups from Europe and Asia perform as well as the majority population within a single generation.[97]

One environmental source of the IQ gap which has been suggested is poor motivation among low scorers. This hypothesis has been disputed by the researcher Arthur Jensen (1998). For example, one such test asks the subject to lift a finger from a depressed button to strike a light when it flashes. When more than one light is offered as a target the task involves a decision of which to hit (i.e. the one which is lit). These tests measure both reaction time (from when the bulb illuminates to when the subject lifts their finger) and movement time (from when the subject lifts their finger to when the subject reaches the bulb). While movement time measurements show no difference, reaction time measurements negatively correlate with IQ scores and show the same performance gaps between races (Jensen 1993; Jensen and Whang 1994). Jensen argues that it is difficult to imagine that people could be motivated during one part of each segment of the test but not motivated during the other, although no correlation between movement speed and intelligence is claimed. The correlation between IQ and reaction time is low (from .20 to .40).

The effects of test construction on minority groups, such as the use of standard English, were examined by the 1996 APA report, which wrote that "controlled studies have shown, however, that none of them contributes substantially to the Black/White differential under discussion here (Jensen, 1980; Reynolds 82 Brown, 1984; for a different view see Helms, 1992). Moreover, efforts to devise reliable and valid tests that would minimize disadvantages of this kind have been unsuccessful."[98] However the language gap still presents a barrier to education through adverse impacts in classroom settings where the need to teach English as a second language to students who come to school speaking AAVE is not commonly recognized.[99]

According Rushton and Jensen 2005, the Coleman report says that "Negligible, and in some cases, negative correlations were found between IQ and variables such as pupil expenditure, teachers' salaries, teachers' qualifications, student/teacher ratios, and the availability of other school professionals".[100] According to Lisa Sanbonmatsu and colleagues, moving families from public housing to neighborhoods with lower poverty rates produces no significant effects on children's test scores.[101]

Genetic explanation

Arthur Jensen and others argue that the Black-White IQ gap is significantly genetic. That is, they argue that the same mix of genetic and environment factors that cause IQ differences among individuals or between families of the same race also causes the differences seen between races. In this view, the genetic contribution to average intelligence differences among races are like average skin color differences: a product of different allelic frequencies within each population. Others are critical of Jensen's methods and evaluation (Sternberg 2005; Suzuki and Aronson 2005; Nisbett 2005).

The results of most (indirect) analyses used to test the genetic hypothesis do not logically contradict a primarily environmental explanation of the lower IQ of Blacks. That is, a plausible (but some argue ad hoc) environmental explanation for the lower mean IQ in Blacks can be offered in most cases.

Arthur Jensen and others[attribution needed] have concluded that the US IQ gap is partially genetic. Rushton and Jensen say that while plausible environmental explanation for the lower mean IQ in Blacks in the U.S. can be offered in many cases, these explanations are less capable of explaining the higher average IQ of East Asians than Whites.

To support their theory, they often cite several arguments and observations:

Black–White–East Asian differences in IQ, reaction time, and brain size are observed worldwide in a range of cultures and environments. In the United States, significant Black-White IQ differences are observable at every age above 3 years, within every occupation or socioeconomic level tested, in every region of the country, and at every time since the invention of ability tests.[102]

Jensen and others[attribution needed] have argued that the magnitude of race differences on different IQ subtests correlate with the extent to which those subtests measures g,[103] which also correlates with measures of the subtests heritability.[104] From these and other findings, they argue that race differences have a partly biological basis.[105]

The rising heritability of IQ with age (within all races; studies have reported on average in the developed world heritability starts at 20% in infants, rises to 40% in middle childhood, and peaks at 80% in adulthood); and studies showing the virtual disappearance (~0.0) by adulthood of shared environmental effects on IQ (for example, family income, education, and home environment), with adopted siblings partaking in the studies no more similar in IQ than with strangers[106] From these studies, they argue that most suggested environmental explanations for IQ difference between groups do not have a strong enough effect on IQ to fully account for group differences.

Studies of US comparisons of both parents to children and siblings to each other finding regression to differing means for different races (85 for Blacks and 100 for Whites) across the entire range of IQs,[107] despite the fact that siblings are matched for shared environment and genetic heritage, with regression unaffected by family socioeconomic status and generation examined[108]

Evidence against test construction and cultural bias: the internal consistency of item difficulty for all groups, the equivalent validity of tests in predicting academic and occupational outcomes for all groups, and the persistence of the IQ gap on relatively culture-free tests.[109]

Other evidence, such as transracial adoption, certain racial admixture studies, behavior genetic modeling of group differences, "life-history" traits, and evolutionary explanations have also been proposed to indicate a genetic contribution to the IQ gaps and explain how these arose.[111] Critics of this view, such as Robert Sternberg, argue that these studies are either flawed and thus inconclusive, or else that they support a primarily environment (<20% genetic) hypothesis.[112] For example, Dolan and Hamaker 2001 argue that the statistical methods linking the Black-White gap to g are insufficient.[113]

According to Linda Gottfredson, a researcher at the University of Delaware IQ differences among individuals of the same race reflect (1) real, (2) functionally/socially significant, and (3) substantially genetic differences in the general intelligence factor (Gottfredson 2005b, p. 311). Also, again according to Dr Gottfredson, average IQ differences among races reflect (1) real and (2) significant differences in the same g factor (Gottfredson 2005b, p. 311). However, it is a matter of debate whether IQ differences among races in a given country are primarily environmental, primarily genetic or simply an artifact of an inaccurate use of social racial identification as a proxy for genetics.[114]

A recent review summarizing the arguments for a genetic explanation can be found here.[115] A critique of genetic explanations can be found here.[116] See also the table below for counter-arguments.

"Heritability" and "Factor X"

"Heritability"

The height of this "ordinary genetically varied corn" is 100% heritable, but the difference between the groups is totally environmental.[117]

Herrnstein and Murray explain a limitation of within-group heritability in The Bell Curve:

As we discussed in Chapter 4, scholars accept that IQ is substantially heritable, somewhere between 40 and 80 percent, meaning that much of the observed variation in IQ is genetic. And yet this tells us nothing for sure about the origin of the differences between races in measured intelligence. This point is so basic, and so commonly misunderstood, that it deserves emphasis: That a trait is genetically transmitted in individuals does not mean that group differences in that trait are also genetic in origin. Anyone who doubts this assertion may take two handfuls of genetically identical seed corn and plant one handful in Iowa, the other in the Mojave Desert, and let nature (i.e., the environment) take its course. The seeds will grow in Iowa, not in the Mojave, and the result will have nothing to do with genetic differences. (Herrnstein and Murray 1994, p. 298.)

There are a number of points to consider when interpreting heritability:

High heritability of a trait within a given group has no necessary implications for the source of a difference between groups.[118][119]

A high heritability does not mean that the environment has no impact on the development of a trait, or that learning is not involved. Vocabulary size, for example, is very substantially heritable (and highly correlated with general intelligence) although every word in an individual's vocabulary is learned. In a society in which plenty of words are available in everyone's environment, especially for individuals who are motivated to seek them out, the number of words that individuals actually learn depends to a considerable extent on their genetic predispositions.[120]

A common error is to assume that because something is heritable it is necessarily unchangeable. This is wrong. Heritability does not imply immutability. As previously noted, heritable traits can depend on learning, and they may be subject to other environmental effects as well. The value of heritability can change if the distribution of environments (or genes) in the population is substantially altered. For example, an impoverished or suppressive environment could fail to support the development of a trait, and hence restrict individual variation. This could affect estimates of heritability.[121] Another example is Phenylketonuria which previously caused mental retardation for everyone who had this genetic disorder. Today, this can be prevented if following a modified diet.

On the other hand, there can be effective environmental changes that do not change heritability at all. If the environment relevant to a given trait improves in a way that affects all members of the population equally, the mean value of the trait will rise without any change in its heritability (because the differences among individuals in the population will stay the same). This has evidently happened for height: the heritability of stature is high, but average heights continue to increase.[122]

According to Jensen 1998b, the complement of the maxim that "heritability within groups does not imply... heritability between groups" is also logically true: that environmentalability (the contribution of environment to phenotypic differences) within groups does not imply environmentability between groups.

"Factor X"

Jensen (1973) argued that because the heritability of IQ is so high and the correlation between environment and IQ is so low, a 15 point IQ gap between Blacks and Whites could be explained by environmental factors alone only if the environmental gap between Blacks and Whites was implausibly immense.

Lewontin (1976) argued that Jensen's conclusion does not follow. He offered the example of two genetically indistinguishable populations of plants, one grown under optimal conditions and another grown under poor conditions. Under those conditions, the heritability of a trait such as height may be 100% within groups but the differences between groups would be entirely environmental.

Jensen writes that to avoid concluding that between group differences are partly-genetic in origin, one must believe either that: (1) similar environmental factors have greater effect between groups than within groups or (2) there are environmental factors that have effects between groups but not within groups. Jensen calls the second alternative Factor X. If group differences were caused by racism (discrimination based on race), then racism would be a "Factor X." Jensen labels this an ad hoc hypothesis that violates Occam's razor.

Dickens and Flynn argue that neither Lewontin nor Jensen is correct. Lewontin is mistaken, he argues, because he posits an implausible Factor X model[123], and they argue that Jensen's model also have implausible implications, such as that the Flynn effect is significantly due to genetic factors. Instead, they propose an alternative model. "Heritability" include not only a direct genetic effect on IQ, but also the effect on environmental factors caused by those with higher IQ seeking out a more stimulating environent. The direct genetic effect can be quite small despite a high "heritability" measure and large IQ differences due to feedback loops between prior IQ and seeking out more stimulating environments. Also, there is no need to have a large Factor X causing permanent effects in IQ. Many small and transient environmental effects that persistently lean in one direction can substitute for a single persistent environmental cause. Averaged together, the total impact can be large, even if each individual effect is small.[124][125] David Rowe and others have both complimented and criticized the published account of the Flynn-Dickens model, which Flynn and Dickens defend.

Shared and nonshared environmental effects

The heritability of intelligence within groups is high. It is widely recognized that within-group heritability does not in itself indicate that between-group differences are genetic in origin, although it is likely a necessary condition. Different kinds of evidence are needed to address the question of between-group heritability. Rushton and Jensen 2005a explain this view:

The cause of individual differences within groups has no necessary implication for the cause of the average difference between groups. A high heritability within one group does not mean that the average difference between it and another group is due to genetic differences, even if the heritability is high in both groups. However, within-groups evidence does imply the plausibility of the between-groups differences being due to the same factors, genetic or environmental. If variations in level of education or nutrition or genes reliably predict individual variation within Black and within White groups, then it would be reasonable to consider these variables to explain the differences between Blacks and Whites. Of course, independent evidence would then be needed to establish any relationship.

According to Loehlin et al. 1975, there is some evidence suggesting lower heritability in Blacks than Whites (e.g., Scarr-Salapatek 1971), but a larger body of evidence suggested equal heritabilities for both races. An analysis of the Georgia Twin Study by Osborne 1980 reported equal heritabilities for both Blacks and Whites.

Two kinds of environmental effects can be distinguished: shared and nonshared effects (see nature versus nurture). Twin and adoption studies, used to measure heritability, can also be used to quantify the two types of environmental effects (Plomin et al. 1977). Shared environmental effects are due to factors experienced in common by all children raised in the same family but that differ among families. Examples of shared environmental effects include socio-economic factors, family cultural practices, and parental influences on children. Nonshared effects are unique for each child, and thus differ among families. Examples include chance events such as accidents, illness, and childhood friends. Anything that happens to one sibling and not to the other contributes to nonshared effects.

McGue et al. (1993) reported (among a population of people studied in the U.S.) that the nonshared environmental effects on IQ remain approximately constant throughout life. Shared environmental effects in their study remained approximately constant (40% to 30%) from 4 to 20 years of age but then drop to zero in adulthood. Genetic factors increase throughout development (from 40% to 50%) but especially after 20 years of age (from 50% to 80%). Plomin et al. (2001) corroborates these results. Environmental factors usually proposed to explain the Black-White gap are shared effects (e.g. social class, religion, cultural practices, father absence, and parenting styles). Jensen (1997) argues that because these effects account for little variance within a race, they are unlikely to account for the differences among races in developed nations.

However, others studies do support that shared environmental factors in developed nations can affect IQ, including IQ gains lasting into adulthood (Capron and Duyme, 1989).[126] However, many such studies measure IQ in children (those shared effects that have disappeared in studies don't disappear until adulthood) or, some critics claim, do not have the controls needed to differentiate genetic and environmental effects. Others argue that some IQ gains disappear exactly because the interventions cease, continuing interventions like Head Start have showed that the IQ gains then remain.

In a re-analysis of adoption data from Capron and Duyme 1989, Jensen 1998a reported that the IQ gains that result from being adopted into high socioeconomic-status homes do not produce gains in g, but only in non-g factors. Jensen also reported that the g factor scores of the adopted children reflected the socioeconomic level of their biological parents, not their adopted parents. This is consistent with Jensen's theory that g is the predominant genetic component of IQ scores; see Spearman's hypothesis below from the relationship between g and racial difference in IQ.

Only shared environmental effects captured in heritability studies disappear in adulthood; more extreme environmental deprivation may likely have a lasting impact on IQ in adults. Heritability only tells us what is the contribution of genes to variation in a trait, not what it could be (Rushton and Jensen 2005). Thus, heritability measures in the U.S. population cannot be extrapolated to populations in developing nations.[attribution needed][How to reference and link to summary or text]

Biased older studies?

Stoolmiller (1999) found that the range restriction of family environments that goes with adoption, that adopting families tend to be more similar on for example SES than the general population, means that role of the shared family environment have been understimated in previous studies. Corrections for range correction applied to adoption studies indicate that SE could account for as much as 50% of the variance in IQ.[127] However, the effect of restriction of range on IQ for adoption studies was examined by Matt McGue and colleagues, who write that "restriction in range in parent disinhibitory psychopathology and family SES had no effect on adoptive-sibling correlations [in] IQ".[128]

According to Eric Turkheimer and colleages (2003), not using an adoption study, the heritability of IQ among young children is lower for poor families, meaning that for poor children environmental influences play a greater role than genetics, which has a contribution close to zero.[129] They suggest that the role of shared environmental factors may have been underestimated in older studies which often only studied affluent middle class families.[130]

Maternal (foetal) environment

A meta-analysis, by Devlin and colleages in Nature (1997), of 212 previous studies evaluated an alternative model for environmental influence and found that it fits the data better than the 'family-environments' model commonly used. The shared maternal (foetal) environment effects, often assumed to be negligible, account for 20% of covariance between twins and 5% between siblings, and the effects of genes are correspondingly reduced, with two measures of heritability being less than 50%. They argue that the shared maternal environment may explain the striking correlation between the IQs of twins, especially those of adult twins that were reared apart.[131]

Bouchard and McGue reviewed the literature in 2003, arguing that Devlin's conclusions about the magnitude of hertiability is not substantially different than previous reports and that their conclusions regarding prenatal effects stands in contradiction to many previous reports.[132] They write that:

Chipuer et al. and Loehlin conclude that the postnatal rather than the prenatal environment is most important. The Devlin et al. (1997a) conclusion that the prenatal environment contributes to twin IQ similarity is especially remarkable given the existence of an extensive empirical literature on prenatal effects. Price (1950), in a comprehensive review published over 50 years ago, argued that almost all MZ twin prenatal effects produced differences rather than similarities. As of 1950 the literature on the topic was so large that the entire bibliography was not published. It was finally published in 1978 with an additional 260 references. At that time Price reiterated his earlier conclusion (Price, 1978). Research subsequent to the 1978 review largely reinforces Price’s hypothesis (Bryan, 1993; Macdonald et al., 1993; Hall and Lopez-Rangel, 1996; see also Martin et al., 1997, box 2; Machin, 1996).[133]

The Dickens and Flynn model

Dickens and Flynn (2001) argue that the arguments regarding the disappearance of the shared family environment should apply equally well to groups separated in time. This is contradicted by the Flynn effect. Changes here have happened to quickly to be explained by genetics. This paradox can be explained by observing that the measure "heritability" includes both a direct effect of the genotype on IQ and also indirect effects where the genotype changes the environment, in turn effecting IQ. That is, those with a higher IQ tend to seek out stimulating environments that further increase IQ. The direct effect can initially have been very small but feedback loops can create large differences in IQ. In their model an environmental stimulus can have a very large effect on IQ, even in adults, but this effect also decay over time unless the stimulus continues (the model could be adapted to include possible factors, like nutrition in early childhood, that may cause permanent effects). The Flynn effect can be explained by a generally more stimulating environment for all people. The authors suggest that programs aiming to increase IQ would be most likely to produce long-term IQ gains if they taught children how to replicate outside the program the kinds of cognitively demanding experiences that produce IQ gains while they are in the program and motivate them to persist in that replication long after they have left the program.[134][135] Regarding the arguments that high IQ people can seek out stimulating environments to increase their IQ, Jensen 1998b has argued that while it's possible to substantially increase IQ through cultural stimulation, the IQ gains are "hollow" with respect to g, and that g itself appears to be a wholly biological variable, and not something that has proven amenable to cultural or psychological manipulation. However, Dickens and Flynn, in the above and later papers, have discussed Jensen's model and rejected it, for example arguing that it implies that the Flynn effect is substantially due to genetic factors.[136]

Spearman's hypothesis

IQ tests contain one or more sets of test questions of different varieties. Individually administered tests often are composed of subtests that have different homogeneous item contents. The mean Black-White difference varies considerably across tests with different contents. For example, the BW gap is larger on tests that require the recall of a series of digits in reverse order than on tests that require the recall of a series of digits in forward order. Across a large number of test, the standardized mean Black-White gap varies from near zero to over one standard deviation. According to Jensen 1998b, "this variation between tests in the size of the standardized mean W-B difference is not explainable in terms of test bias or in terms of differences in types of item content or other formal or superficial characteristics of the tests."

The English psychologist Charles Spearman, in his 1904 book, General Intelligence - Objectively Determined and Measured, described his two-factor theory of intelligence, using statistics. The theory is still used today by researches such as Jensen. It states that individual differences in the general intelligence factor, g, and its various biological correlates (e.g., the volume of gray matter in the frontal cortex) are partly caused by genetic differences between individuals. g has the highest measured heritability of any cognitive ability factor. Jensen formulated a hypothesis now referred to as Spearman's hypothesis which states that the degree of difference between black and white cognitive test scores will be correlated with the degree to which the test measures g (called the test's g-loading). Spearman's hypothesis has a strong form, which says that all test-score differences can be traced to g, and a weak form, which claims that some but not all differences are due to g.

neurophysiological variables, such as average evoked potential (AEP) habituation and complexity and glucose metabolic rate measured by PET scan

average reaction time in elementary cognitive tests

the size of the White-Black difference in test scores

Paleontologist Stephen Jay Gould rejected that idea that IQ is measures "general intelligence"; (or g). Gould's writings about g are disputed by many scholars, including statistician David J. Bartholomew[138] and Arthur Jensen. According to Jensen 1998b "Virtually all present day researchers in psychometrics now accept as a well established fact that individual differences in all complex mental tests are positively correlated, and that a hierarchical factor model, consisting of a number of group factors dominated by g at the apex (or the highest level of generality), is the best representation of the correlational structure of mental abilities."

Dolan and Hamaker 2001 have reanalyzed the data from several previous studies (Jensen and Reynolds 1982; Naglieri and Jensen 1987) that used the statistical method invented by Jensen (the method of correlated vectors) with a more recent and improved method (multigroup confirmatory factor analysis). "On the basis of the present, as well as other results (Dolan, 2000), we are convinced that the Spearman correlation cannot be used to demonstrate the importance of g in b-w differences with any confidence." and "It is possible that the analysis of all available data sets (perhaps using an appropriate meta-analytic procedure) will demonstrate that a model incorporating the weak version of Spearman's hypothesis provides the best description of the data. However, until this work is undertaken, we cannot accept Spearman's hypothesis as an "empirically established fact"[139]

Similarly, in a group paper Famous artefacts: Spearman's hypothesis. Author's reply researchers reported that positive correlations predicted by Spearman's hypothesis are likely only psychometric artefacts which also arise with measures which have nothing to do with 'general ability', for example, the number of toys or books a child has. In fact, these positive correlations will arise with any set of moderately correlated random data, once the sample is split into high and low groups.[140] Zack Z. Cernovsky has said that "Hasty and eager acceptance of weak, biased, and unrepresentative data as scientific evidence of genetically based and relatively immutable racial differences in human potential amounts to psychological warfare on oppressed racial groups."[141] and that it "causes major psychological harm to millions of black children and adults (with respect to self-esteem, career expectations, interracial relationships, etc.".[142]

Gene-environment interactions

Minority-specific effects on intelligence arising from cultural background differences between the races would be expected to affect the correlations between the measures of environmental background variables and outcome measures. Rowe et al. (1994) compared cross-sectional correlation matrices using both independent variables (e.g., home environment, peer characteristics) and developmental outcomes (e.g., achievement, delinquency). Rowe et al. (1995) compared correlations between academic achievement and family environment. They reported that the covariance matrix of each group were equal. That is, they failed to find evidence for distortions in the correlations between the background variables and the outcome measures that would suggest a minority-specific developmental factor. Similarly, Carretta (1995), Owen (1992), and Rushton et al. (2000), Rushton et al. (2002), Rushton et al. (2003)) reported nearly identical statistical structure on psychometric variables in each group. The factor structure of cognitive ability is nearly identical for Blacks and for Whites; there were no race-specific factors.

Using structural equation modeling Rowe and Cleveland (1996) estimated the genetic architecture for Black and White siblings. They reported that the best-fitting model for the source of differences between and within races was the same: both genetic and environmental factors. Jensen 1998b (p. 465) reanalyzed a subset of this data. This analysis reported that the Black-White IQ difference was best explained by a model of both genetic and environmental factors, and that the genetic-only and the environmental-only models were inadequate.

Nichols (1972) using differential heritabilities among Blacks and Whites and later Rushton (1989) using inbreeding depression calculated in Japan reported that the Black-White gap is least on IQ subtests most affected by the environment, and greatest on subtests that are least affected by the environment. It is difficult to attribute the relationship between inbreeding depression from Japan with the Black-White IQ gap in the U.S. to an environmental (not-genetic) cause.

See also the table below for counter-arguments.

Null hypothesis

Discussion of alternative explanations in science, including alternative explanation of race differences in average IQ, often make reference to the concept of a null hypothesis against which an alternative hypothesis is being tested.

For example, when testing the hypothesis that genetic factors contribute to the Black-White gap, the null hypothesis according to Loring Brace is:

"the same level of intellectual capability ought to have evolved in all human groups" (Brace, 1999a)

Loring Brace writes, "Jensen, however, has labeled this the 'egalitarian fallacy,' adding that it is 'gratuitous' and 'scientifically unwarranted' (Jensen, 1980:370)".[143]

Jensen responds, saying that "Brace's ad hominem criticism and nihilistic stance regarding key concepts in my book (Jensen 1998, 1999), particularly the g factor and race, as I have carefully defined these terms, can serve only one useful purpose: It gives present-day readers a view of one of the remote outposts of the 1970s style of attack by the ideologically committed opponents of my position 30 years ago."[144]

Jensen states the proper null hypothesis should be the existence of differences along the same lines as those that exist within groups (Jensen, 1998:444):

the distribution of B-W differences in g results from the same mix of genetic and nongenetic factors that cause the distribution of individual differences in g within each group. Thus group differences in g are viewed simply as aggregated individual differences.[145]

Another description of comparing alternative hypotheses relates to Bayesian probability, relating to the concept of a prior probability. According to David Rowe, "in science, viable, alternative hypotheses are ideally given equal Bayesian prior weights;... researchers should regard the prior probability of a genetic hypothesis being true as about the same as that of an environmental hypothesis being true."[146]

Arguments against the genetic explanation

Although the vast majority of researchers who support a primarily environmental explanation for the test score gap between races acknowledge that abilities related to high performance on tests may be heritable for individuals they generally do not agree that this idea makes sense when comparing large groups or races. Many potential flaws in research that supports the genetic hypothesis have been named and there are objections to all the arguments raised above (see table below).

Nisbett (2005) argues that the most direct sort of evidence relates to the influence of European ancestry on Black intelligence. U.S. “Black” populations contain as much as 30% European genes. This means that an individual who is identified as Black could have anywhere from 100% African ancestry to mostly European ancestry (true of as much as 15% of some U.S “Black” subpopulations; Herskovits, 1930). This allows us to identify the extent to which percentage African ancestry, variously assessed, is associated with IQ. Such assessments include studies on skin color, self-reported ancestry, European blood groups, and studies on mixed race children. Nisbett states: "The most directly relevant research concerns degree of European ancestry in the Black population. There is not a shred of evidence in this literature, which draws on studies having a total of five very different designs, that the gap has a genetic basis."[147] Dickens (2005) states that "Although the direct evidence on the role of environment is not definitive, it mostly suggests that genetic differences are not necessary to explain racial differences. Advocates of the hereditarian position have therefore turned to indirect evidence...The indirect evidence on the role of genes in explaining the black-white gap does not tell us how much of the gap genes explain and may be of no value at all in deciding whether genes do play a role. Because the direct evidence on ancestry, adoption, and cross-fostering is most consistent with little or no role for genes, it is unlikely that the black-white gap has a large genetic component."[148]

Another recent theory hypothesizes that fluid cognition (gF') may be separable from general intelligence, and that gF' may be very susceptible to environmental factors, in particular early childhood stress. Some IQ tests, especially those used with children, are poor measures of gF', which means that the effect of the environment on intelligence regarding racial differences, the Flynn effect, early childhood intervention, and life outcomes may have been underestimated in many studies. The article has received numerous peer commentaries for and against.[149]

Many studies that attempt to test for heritability find results that do not support the genetic hypothesis.[150] They include studies on IQ and skin color,[151] self-reported European ancestry,[152] children in post WWII Germany born to black and white American soldiers,[153] blood groups,[154] and mixed-race children born to either a black or a white mother.[155] Many intervention and adoption studies also find results that do not support the genetic hypothesis.[156] Non-hereditarians have argued that these are direct tests of the genetic hypothesis and of more value than indirect variables, such as skull size and reaction time.[157] Hereditarians argue that these studies are flawed due to their age, lack of replication, problems with their sample population, or that they do in fact support the genetic hypothesis.[158]

Fryer and Levitt 2006, with data from "the first large, nationally representative sample" of its kind, report finding only a very small racial difference when measuring mental function for children aged eight to twelve months, and that even these differences disappear when including a "limited set of controls".[159] They argue that their report poses "a substantial challenge to the simplest, most direct, and most often articulated genetic stories regarding racial differences in mental function."[159] They conclude that "to the extent that there are any genetically-driven racial differences in intelligence, these gaps must either emerge after the age of one, or operate along dimensions not captured by this early test of mental cognition."[159]

Comparison of explanations

The Black-White IQ gap in the U.S. may be explained by a variety of explanations on various axes of dispute. There are questions as to the magnitude, direction and causes of gaps, as well as questions regarding the fundamental assumptions of how to frame the question.

This table includes arguments put forward by a wide variety of sources on a wide variety of positions, and also includes some rebuttal and counter-rebuttal on those arguments. Neither column represents a single major point of view.

Adoption and admixture

Some Black-White-East Asian differences in IQ (both positive and negative) remain following transracial adoption. Burrow and Finley (2004) reported Black-White-East Asian differences in cognitive and psychological variables among adolescents adopted by white families. They also found that Black-White mixed-race children fell in between the White and Black averages. Two studies of Asian children adopted by White families reported average IQ scores in the adopted Asian children that are higher than Whites.(Clark and Hanisee 1982; Frydman and Lynn 1989.

Nisbett (2005) reports the results of the three three major adoption studies that address the question of genetic contribution to the Black-White IQ difference. Two of the studies shows unambiguous lack of support for the hereditarian model and one study showing at most ambiguous support for it.[160] Several other adoption studies finds no IQ difference between Whites and East Asians.[161]

Rushton and Jensen 2005b argue that these studies are "peculiarly old, the mean year of publication being 1960" and "actually very weak and nondecisive, not having been replicated even once". No studies of Black-White genetic admixture have been performed with the multi-locus DNA sequencing required to make reliable conclusions. Lynn (2002) reports that skin color is corrlated with intelligence among African Americans.

There are numerous studies of the association between skin color and IQ. The correlation between lightness of skin and IQ, averaged over a large number of studies reviewed by Shuey (1966), is very low (0.1). The average correlation between IQ and judged “Negroidness” of features is even lower.

A 2002 reanalysis of Lynn's data concluded "that his bivariate association disappears once childhood environmental factors are considered. Therefore, a genetic link between skin color and intelligence among African Americans cannot be supported in his data."[163]

IQ have very low positive to low negative correlation with several studies concerning the degree of European blood groups, or self-reported degree of European ancestry among Blacks.
[164]

While this study shows hybridized White children scoring only 0.5 IQ points lower than unmixed White children when birthed and raised by German mothers, Jensen 1998b notes that sampling error may have made the results unreliable (for example unmixed White boys scored 4 points higher than hybridized White boys, but unmixed White girls scored 3 points lower than their hybridized counterparts; unmixed White girls scored 8 points lower than unmixed White boys despite the fact that these groups were identical on the test's standardization sample) and the effects of hybrid vigour may have elevated the mixed race children by about 4 IQ points and selective preferences on the part of German mothers may have made the Black and White fathers especially similar[165]. Rushton & Jensen (2005) point to three other factors which may have elevated the IQ's of the mixed race children: "One third of the children were between 5 and 10 years of age, and two thirds were between 10 and 13 years...behavior genetic studies show that while family socialization effects on IQ are often strong before puberty, after puberty they dwindle, sometimes to zero. Second, 20% to 25% of the “Black” fathers were not African Americans but French North Africans (i.e., largely Caucasian or “Whites” as we have defined the terms here). Third, there was rigorous selection based on IQ score in the U.S. Army at the time, with a rejection rate for Blacks on the preinduction Army General Classification Test of about 30%, compared with 3% for Whites." [166]

A study which "examined the IQs of several hundred German children fathered by Black GIs during the post-1945 occupation and compared them with the IQs of children fathered by White GIs. The children of the Black GIs had an average IQ of 96.5. The children of the White GIs had an average IQ of 97." Some, like the American Psychological Association, consider this study be strong evidence against the genetic explanation.[167] Because the Black-White gap in the military was similar to that for the U.S. population, these data imply that the Black-White gap in the U.S. population as a whole is not genetic, even in part (Flynn, 1980, pp. 87-88). The results seem particularly telling because it seems highly likely that environmental conditions were inferior for Black children. He argues that "one would have to assume preposterously high IQ scores on the part of the North African portion of the Black fathers to make up for the substantial difference between offspring of Blacks and Whites predicted by their hereditarian theory. Second, Rushton and Jensen assume that Black soldiers were more rigorously selected than Whites and so might have had IQs nearly as high as those of the White soldiers. Blacks in the military did indeed have higher IQs than did Blacks in the general population, but the same was true of White soldiers compared with the general White population. Flynn (1980) has argued that the evidence indicates that the gap in IQ between Black and White soldiers was the same as that in the U.S. population at large."[168] Regarding heterosis Flynn points out that it is breeding with close relatives, such as in isolated and small rural communities, that depresses IQ. Rregarding the beneficial effects of outbreeding, 3 IQ points is the advantage of not breeding with one's cousins.[169] Regarding the argument about the disappearance of the shared family effect, see for example Dickens (2005) for a rebuttal.

Because the White mother-Black father pairs averaged 1 year more of education than the Black mother-White father pairs, the study is uninterpretable.

If the Black-White IQ gap is largely hereditary, then children having one Black and one White parent should have the same IQ on average, regardless of which parent is Black. But if one assumes that mothers are particularly important to the intellectual socialization of their children and if the socialization practices of Whites are more favorable to IQ development than those of Black mothers, then children of White mothers and Black fathers should have higher IQs than children of Black mothers and White fathers. This could of course not have a plausible genetic explanation. In fact, it emerges that children of White mothers and Black fathers have IQs 9 points higher than children with Black mothers and White fathers (Willerman, Naylor, & Myrianthopoulos, 1974). This result in itself suggests that most of the Black-White IQ gap is environmental in origin. But because mothers are not the only environmental influence on the child's IQ, the 9-point difference might be regarded as a very conservative estimate of the environmental contribution to the gap. There can be no basis for assuming that 1-year's difference in education on the part of the parents could possibly translate into an expected 9 IQ point difference for the children.[170]

Utility of racial categories

Some geneticists argue categories of self-identified race/ethnicity or biogeographic ancestry are both valid and useful.[171] They emphasize the continental origin of major races: “namely, African, Caucasian (Europe and Middle East), Asian, Pacific Islander”. For other groups "a decision to split or lump smaller populations into racial groups will depend on the focus of a research question."[172] They find that these categories correspond with clusters inferred from multilocus genetic data..[173] Moreover, they conclude that this correspondence implies that genetic factors might contribute to unexplained phenotypic variation between groups.[174] In the 1985 survey reported by Leiberman and colleagues, only 16% of biologists reject the concept of race. In response to claims such as "there are no human races," Ernst Mayr, one of the 20th century's leading evolutionary biologists, said "Those who subscribe to this opinion are obviously ignorant of modern biology."[175] Risch and colleagues (2002) argue that "much of this discussion does not derive from an objective scientific perspective."[176] In response to claims that race does not exist, geneticst A.W.F. Edwards quotes Fischer: "that the best causes tend to attract to their support the worst arguments, which seems to be equally true in the intellectual and in the moral sense."[177]

Modern anthropologists use clines as an alternative to "races", with variation occurring gradually across geographic areas, instead of social constructs of "race". "By 1985 anthropology's core concept of "race" had been rejected by 41% of physical anthropologists and 55% of cultural anthropologists [Lieberman 1968; Lieberman, Stevenson, and Reynolds 1989:69]. A similar survey in 1999 reported that the concept of race was rejected by 69% of physical anthropologists and 80% of cultural anthropologists (Lieberman and Kirk n.d.)"[178]

"As the 20th century reached its end, a paradox emerged in which, while most anthropologists had come to reject concepts of biological races and racism (Lieberman and Kirk n.d., Lieberman, Stevenson, and Reynolds 1989), a number of psychologists persisted in the “race” idea and the “scientific” racism that had prevailed in the 19th and much of the 20th century (Herrnstein and Murray 1994; Lynn 1977a, b; Rushton 1988b)."[178]

"During the last hundred years, the debate over the meaning of race has retained a highly consistent core, despite evolution of the technical details...Each time the technical facade of these racialist arguments is destroyed, the latest jargon and half-truths from the margins of science are used to rebuild them around the same core belief in Black inferiority. No technology—even the awe-inspiring tools now available to DNA science—can overcome the handicap of fundamental conceptual errors. Race is not a concept that emerged from within modern genetics; rather, it was imposed by history, and its meaning is inseparable from that cultural origin."[114]

"Race, a quantitative distinction within a species, has no equivalent defining criterion—that is, genetic variability is not restricted to discrete packages (American Anthropological Association [AAA], 1998). This aversion to distinctions without meaning is what has led most geneticists and anthropologists to the conclusion that race in its common usage has no biological basis (AAA, 1998; Darwin, 1871/1981; Gould, 1996; Graves, 2001; Kittles & Weiss, 2003; Lewontin, 2000; Mayr, 1996; Montagu, 1964; Templeton, 1998)."[114]

"This point bears restating: To cluster individual members of a species into groups is not the same as creating a natural biological category. One could cluster humans into an infinite number of fractal units based on size (family, clan, deme, continent, etc.) or on a physical trait (height), and the meaning of those groupings would vary in an infinite number of ways."[114]

"This assertion is both counter-intuitive and factually incorrect.... If it were true, it would be impossible to create discrete clusters of humans (that end up corresponding to the major races).... Two Caucasians are more similar to each other genetically than a Caucasian and an Asian."[179]

"Genetic data ... show that any two individuals within a particular population are as different genetically as any two people selected from any two populations in the world."[180]

"From the hereditarian perspective, why then would IQ not be expected to vary between, say, Sicilians and Swedes as much as between Europeans and Africans?"[114]

IQ differences

Black-White-East Asian differences in culture-fair IQ test scores exist world-wide despite international differences in social, cultural, and economic conditions.[181]Lynn 1987, among others, argues that higher IQ scores among East Asians (living in East and South Asia) than Whites (living in North American and Europe) is seen as a challenge for primarily environmental theories because standards of living in Asia are lower than or equal to those in North America or Europe. For example, average IQ scores are higher in the People's Republic of China (Lynn and Vanhanen 2002) than for African Americans even though per capita GDP (PPP) is lower in China ($5,000 as of 2003) than per capita African American income ($15,583 as of 2003) (DeNavas-Walt et al. 2004).

The only nationwide IQ tests have been done in a few developed countries, and the attempted aggregations of smaller studies in other nations, most of which do not have any all, have been severely criticized, see IQ and the Wealth of Nations.

Regarding China and African Americans, and developing vs. developed nations more generally, there are numerous environmental and social factors which could differ, such as those mentioned elsewhere in this article. For example, child-rearing practices and attitudes differ greatly between East Asians nations and the US.[182] Many East Asian nations have a high consumption of fish. Fish oil supplementation to pregnant and lactating mothers has been linked to increased cognitive ability.[183] See also Health and intelligence.

Sub-Saharan Africans have an average IQ of 70 (Rushton 1996a), supported by data using Raven's Progressive Matrices. Jensen (1998b) discusses his observation among California children that very low IQ Blacks are qualitatively normal in social and motor skills, but perform no better than Whites with equally low IQ on cognitive tasks except those that require rote memorization, where "mentally retarded" Blacks do significantly better than Whites. He speculates that 12.5% of cases of IQ <70 are due to organic defects in Blacks, compared to 50% in Whites, giving the impression that low IQ Whites are more handicapped than low IQ Blacks.

One argument of many against the reliability of the IQ scores in developing nations is that in some such countries a majority of the population would be classified by the IQ scores as mentally retarded. People with a score below 75 will often, but not always, have difficulties with daily living skills, which would include the majority of people in Sub-Saharan Africa, arguably absurd. The most extreme exampke is Equatorial Guinea is one of the few African nations that actually have a study and is classified as having the lowest average IQ in the world, 59, based on study of 48 persons 10-14 years old. A large proportion of the population should also be classified as moderately (<16%) and severely (<2%) mentally retarded. In the U.S., the moderately mentally retarded require moderate supervision and the severely mentally retarded often have other physical disabilities and may thus require constant supervision, be unable to provide for themselves, be unable to speak long sentences, and, in many cases, be unable to do things like getting dressed without help.

Several studies argue that the Black-White IQ gap in the US has remained constant at approximately one standard deviation since it was first measured despite social and economic change during that time, including the civil rights movement and Brown v. Board of Education.[184]

Average IQ scores gaps internationally have been stable since they were first measured in the early and mid 20th century.[185](Lynn and Vanhanen 2002 ).

Moreover, the extent of concrete social and economic change is debatable; for example, Jonathan Kozol, in his 2005 book Shame of the Nation, reported that public schools are more racially segregated today than they were in 1969.

Considering the few studies outside some developing nations, and other problems as described in the article about IQ and the Wealth of Nations, any claim regarding an internationally stable gap is doubtful. The given source, [6], a blog site, is highly questionable considering the absence of the Flynn effect in the graph.

Some studies find that the three-way difference in average IQ can be measured in very young children and before the start of schooling. For example, a one standard deviation gap is observed in Black and White 3-year olds matched for gender, birth order, and maternal education (Peoples et al. 1995). Lynn 1996 reported that by age 6 the average IQ of East Asian children is 107, 103 for White children and 89 for Black children. Broman et al. (1987) reported that the same trichotomy in brain size and IQ held at 4 months, 1 year, and 7 years of age.

A recent, large, and nationally representative data set find only very small (0.06 SD between whites and blacks) racial differences on measures for mental function for children aged eight to twelve months. These differences disappear when controlling for a limited set of factors such as differences in SES. "These findings pose a substantial challenge to the simplest, most direct, and most often articulated genetic stories regarding racial differences in mental function." "To the extent that there are any genetically-driven racial differences in intelligence, these gaps must either emerge after the age of one, or operate along dimensions not captured by this early test of mental cognition."[186]

Environmental factors can affect very young children and affect black and white children differently, for example breastfeeding and environmental toxins such as lead, as discussed in other sections in this article. In developing nations there are factors affecting children, like severe malnutrition and tropical diseases, not present in developed nations, see Health and intelligence.

One statistical analysis suggests that the Flynn effect is qualitatively different than the Black-White IQ gap (Wicherts et al. 2004).

The Flynn effect is the finding that IQ scores have been increasing very rapidly worldwide, in particular on "culture-fair" and highly g-loaded tests such as Raven's Progressive Matrices. Average IQ in the US in 1932 was 80, well below the current black-white gap. Many environmental influences has been suggested as an explanation, and it seems not unlikely that the effect started earlier and may end sooner for Whites in the US compared to Blacks and for developed nations compared to developing nations. This may happen regardless of whether the gaps have been stable or not until now.

The Wicherts study refers to "measurement invariance", is not a statement about the role of genetics in the B-W gap, and is a relatively minor statement that not mentioned in the abstract.

American Blacks have a lower average IQ than Hispanic and Native American groups, which are more socio-economically deprived. For example, the Inuit, who live in the Arctic, have higher average IQs than North American Blacks (Berry 1966; MacArthur 1968) despite being extremely poor (Vernon 1965; Vernon 1979).

That Blacks are less socioeconomically deprived than Hispanics is incorrect, see Household income in the United States. The Inuit (Eskimo) cannot be directly compared to the US population, for example they have substantially different nutrition from eating large amounts of fish.[187] Fish oil supplement to pregnant and lactating mothers has been linked to increased cognitive ability, see Health and intelligence.

?

Results from the US, which include almost all studies and findings, cannot be generalized to the world as whole. Blacks, East Asians, Hispanics, and Whites in the US are not a random sample of the worldwide popultion. The environment in the US differs from other nations. For example, some studies find that the Black-White gap in the UK is about half that in the US.[188] In developing nations there are many factors, like severe malnutrition and certain diseases, that affect IQ that are not present in developed nations.

Theories holding that Blacks score lower than Whites because of test bias would predict that Asians would also score lower than Whites. However, the reverse is true.

Assuming that test bias must negatively affect scores of any minority group is unsupportable. Asians and Blacks do not share the same environmental or cultural influences.

Ashkenazi Jews have often been persecuted and discriminated against, but they still display the highest average IQ of any ethnic group, as well as SAT scores higher than those of non-Jewish Caucasians. Rowe 2005, pp. 67-68 argues that this counters arguments that depressed IQ scores of African Americans are due to discrimination or prejudice. Similarly, Jensen 1998b, p. 510, points to the examples of Chinese, Japanese, Jews, and East Indians, stating that they have been minorities, discriminated against, or even persecuted, yet do not do poorly on g-loaded tests. Murray and Herrnstein 1994 make similar arguments.

Jews and East Asians have been discriminated against in the past, but arguably far less now, compared to African Americans.

Persecution and discrimination is not always applied in identical ways with identical effects. Conflating the terms "discrimination" and "prejudice" as having both the same meaning as well as effect is a logical fallacy. Neither do persecution and discrimination encompass the entirety of culture or environmental effects.

Rowe is particularly criticized for "misuse of broad scientific concepts and incorrect or biased misinterpretation of specific scientific data."[189]

Dichotomy in intelligence is entirely compatible with various all environmental explanation. For example, East Asians may have higher spatial ability for example due to their use of logographic writing systems.

One study found that g does not differ between Greek and Chinese pupils. The Chinese did outperform the Greeks in visuo/spatial ability, but this difference was smaller at earlier ages, grew during the first years of schooling and decreased later. The authors suggest that this pattern can be explained as follows: the Chinese students train their visuo/spatial ability during their early school years, as they have to learn many logographic characters of the Chinese writing system. Later in life, the Greek students adopt compensating strategies to deal with visuo/spatial information, and therefore the difference decreases.[190]

Again, there are numerous possible environmental explanations, like greater emphasis on spatial ability rather than verbal ability among hunter-gatherers.

Claimed attributes of the US black-white gap not compatible with only environmental factors

"The g-based factor hierarchy is the most widely accepted current view of the structure of abilities"[17] Correlations between an IQ subtest's g-loading, and the magnitude of the Black-White-East Asian score gap for that subtest (Peoples et al. 1995; Jensen 1993 pp. 47-8; Rushton 1995 pp. 138-9). For example, the Black-White gap is greater on backward digits span (a test where subjects repeat digits in the reverse order that they are given, and the more g-loaded test) than forward digits span (a test where subjects repeat digits in the same order that they are given, and the less g-loaded test). As predicted by Spearman's hypothesis, the B-W gap is largest on the most g-loaded tests. Narrowing of the B-W gap has been seen mostly on less g-loaded tests, such as literacy tests.[192] Arthur Jensen argues that there is no independent evidence that the environmental explanations commonly given for the Black-White gap (for example, "past history of slavery", discrimination, "caste status", "peer pressure against 'acting white'", etc) have an effect on g (Jensen 1998b, p. 510).

The author of multiple factor analysis, L. L. Thurstone (1947), warned "we must guard against the simple, but common, error of merely taking a first centroid factor, a first principal component, or other mean factor, in a test battery and then calling it a general factor". "Spearman's g, then, is a "statistical artifact." (C. Loring Brace, 2001)

Dolan and Hamaker 2001 have reanalyzed the data from several previous studies (Jensen and Reynolds 1982; Naglieri and Jensen 1987) that used the statistical method invented by Jensen (the method of correlated vectors), in turn used for many studies regarding g, with a more recent and improved method (multigroup confirmatory factor analysis). "On the basis of the present, as well as other results (Dolan, 2000), we are convinced that the Spearman correlation cannot be used to demonstrate the importance of g in b-w differences with any confidence." and "It is possible that the analysis of all available data sets (perhaps using an appropriate meta-analytic procedure) will demonstrate that a model incorporating the weak version of Spearman's hypothesis provides the best description of the data. However, until this work is undertaken, we cannot accept Spearman's hypothesis as an empirically established fact"[139] This leaves the validity of Spearman's hypothesis, considered a central justification for the genetic explanation, an unresolved question.

Correlations between an IQ subtest's heritability or inbreeding depression and the magnitude of the Black-White-East Asian score gap for that subtest (Rushton 1989a). Environmental theories would predict the opposite.[193]

Theories holding that Blacks score lower than Whites because of test bias would predict the Black-White gap would be smaller on culture-reduced tests than on culture-loaded tests. Yet the reverse is true (Murray and Herrnstein 1994).

Outdated methodology. If anything, the results show that test bias exists.[195]

Rising heritability of IQ with age, and decreasing shared-family effects (e.g., socioeconomic factors) on IQ after adolescence. An environmental cause of the IQ gap is seen as necessarily being a shared family effect.

See the section on heritability at the beginning of the article.

Regarding the disappearance of effects from the shared family environment seen in US studies, see the section on this above. In brief, there are alternative models incorporating the shared maternal (foetal) environment that may better fit the available data, more recent studies suggest that earlier studies may have been biased, and the Dickens and Flynn model allow very large environmental influences also for adults.

Studies using structural equation modeling find results consistent with the partially-genetic explanation (Jensen 1998b, pp. 464-467). Studies suggesting that IQ heritability and gene-environment interactions within races are the same for Blacks and Whites. That is, no race-specific statistical factors, such as an effect of White racism, have been identified in such analyses. The IQ gap exists even among middle- and upper-class Black and White families where within-race heritabilities are high and shared family effects are near zero.

Dickens (2005) argues that the same arguments can be applied to the Flynn effect to show that the large and rapid US gain in IQ scores is substantially due to genetic factors which is extremely unlikely. He and Flynn have instead presented an alternative model explaining such contradictions. He argues that it is unlikely that the black-white gap has a large genetic component.[196]

There are many factors that can affect IQ that differ between Blacks and whites, for example breastfeeding and blood lead levels, as noted elsewhere in this article.

Many older studies have only studied middle class families but SES has recently been shown to be relatively more important in poorer families.[197]

Several studies have shown that environmental differences between blacks and whites can, in a statistical sense, “explain” nearly all of the difference in cognitive ability between black and white children.[198]

Studies of US comparisons of both parents to children and siblings to each other finding regression to differing means for different races (85 for Blacks and 100 for Whites) across the entire range of IQs despite the fact that siblings are matched for shared environment and genetic heritage, with regression unaffected by family socioeconomic status and generation examined.[199] For example, the children of wealthy, high IQ Black parents score lower than the children of poor, low IQ White parents (Jensen 1998b, p. 358); and for Black and White children with an IQ of 120, the siblings of the Black children average an IQ of 100 whereas the siblings of the White children average an IQ of 110; in comparison, for Black and White children with an IQ of 70, the siblings of the Black children average an IQ of 78 whereas the siblings of the White children average an IQ of 85 (Jensen 1973, pp. 107–119))

Does not exclude environmental explanations, it may only make them more difficult.[200]

Possible differences in brain size and other correlates of IQ

In a meta-analysis of 37 studies, McDaniel 2005 concluded that total brain size correlates with intelligence. Among adults of the same sex, the average correlation is approximately 0.4. The correlation between brain size and IQ seems to hold for comparisons between and within families (Gignac et al. 2003; Jensen 1994; Jensen & Johnson 1994). However, one study reported no such family-related connection (Schoenemann et al. 2000). The volume of specific brain structures also correlates with IQ. Genetics are known to influence brain structure (Thompson et al. 2001) and some aspects of cognition (Berman and Noble 1995). In one study, the correlation between gray matter volume and g is reported to be mediated entirely by genetic factors (Posthuma et al. 2002). A review in Nature Reviews Neuroscience noted "Correlations between intelligence and total brain volume or grey matter volume have been replicated in magnetic resonance imaging (MRI) studies, to the extent that intelligence is now commonly used as a confounding variable in morphometric studies of disease."[201]

These studies do not not refer to racial differences. A correlation of 0.4 explains only 16% of the variance.

Black-White-East Asian differences in brain size and other physiological variables (such as skull structure, and degree of convolution of the brain) in the United States and a few other developed countries (e.g. UK, Japan). (Rushton, 1990:786). Skull sizes of different races have been compared since the 1800s (Morton, 1849), showing differential sizes which are assumed related to IQ (Rushton, 1996).

In principle, assuming brain size and IQ are related, then all environmental factors that can affect IQ can also affect brain size. Better nutrition can affect brain growth, as can cognitive stimulation. A larger brain is not by itself evidence for genetics any more than IQ scores are. See the article regarding the Flynn effect for studies showing that brain and skull size has been increasing.

The study cited by Rushton (Beals, Smith, and Dodd 1984) actually finds that climate variables are strongly correlated with cranial variation, where as "race" had low correlations. The views of Morton and Rushton have been invalidated "by a century of anthropological research" (Gossett 1965, Cravens, 1978), and themselves are inconsistent with each other (Morton putting "Caucasoids" as the group with the largest brains, and Rushton putting "Mongoloids" as the group with the largest brains).

The only study cited as evidence for race differences using MRI is an old study primarily looking at a small sample of subjects with serious mental disease (Harvey et al. 1994).

In addition, some researchers have argued from studies in siblings that IQ affects socioeconomic status, rather than the other way around (Murray 1998). Studies which simultaneously control for dozens of social and economic conditions are uninformative because they assume that such differences are the cause rather than the consequence of IQ differences (Murray and Hernstein 1994; Murray 2000). Neisser et al. concluded "it is clear that no model in which 'SES' directly determines 'IQ' will do."[17]

One study found that adjustments for socioeconomic conditions almost completely eliminate differences in IQ scores between black and white children. The remaining difference is statistically insignificant.[202]

A 2002 study looked at how much of the correlation between parent and offspring income different factors accounted for. It found that the offspring's inheritance of wealth, inheritance of a high status race, and having received more years of schooling are important factors, but having received a higher IQ is not a major contributor and having received a higher IQ due to genetics is even less important.[203]

Neisser et al. suggested several other environmental factors, such as being a caste-like minority.

As for brain size, the correlation explains very little of the variance. Similarly, differences in reaction time is by themselves not evidence for genetics and could, for example, be caused by differences in nutrition.

Racial differences in biological characteristics such as myopia that correlate with g. Myopia is more common in Asians and Jews than in Whites, and more common in Whites than in Blacks. Myopia is about twice as common in Jews than in Gentiles. Myopia is likely pleiotropic with g (i.e., myopia and g are caused by the same genes). Arthur Jensen argues that this supports the partially-genetic explanation. (Jensen 1998b, p. 487-489)

A correlation between IQ and myopia can have other causes than genetics. For example, high IQ and reading may be associated, which increase the risk for myopia. The prevalence of myopia has recently increased, suggesting an environmental influence. While there may also be a genetic component to myopia, this is not necessarily evidence for racial genetic differences in IQ.[204] A strong genetic association would greatly decrease the value of intelligence in a societies without glasses.

The cultures of involuntary, nonimmigrant minorities

Some argue the cultures of involuntary, nonimmigrant minorities‌, such as blacks who live in the inner city poses a barrier to education and achievement.

The fear of being accused of "acting white" causes a social and psychological situation which diminishes black students' academic effort and thus leads to underachievement.[205]

Multicultural education, that merely includes content to address culture differences will not work.

Cultural frames of reference for involuntary nonimmigrant minorities such as inner-city blacks are oppositional to the cultural frame of reference of American mainstream culture.

Mainstream cultural values must be reframed for these young people to allow assimilation in to the broader culture otherwise they will remain opressed.[206]

Others suggest that the rejection of the culture involuntary, nonimmigrant minorities is the source of alienation and the cause of gaps in tests scores.

The expectations of inner-city youth which suggest that educational and occupational success are improbable for inner-city residents, are accurate. Racism still exists. If their opportunities were to improve, their cognitive expectations would change and most would be committed to taking advantage of these new opportunities.[207]

Because both liberal and conservative agendas operate within an ideology of White supremacy, both have been inadequate in addressing cultural racism.[208]

The majority culture must become multicultural acknowledging the cultures and values of all people including involuntary or nonimmigrant minorities.

Importance of socioeconomic factors vs. racism

Some researches argue that the effects of racism are a significant contributor to the gap. They write that efforts to close the gap should focus on addressing this issue.

Reserch in to intervention methods to address the problems posed by stereotype threat have had some success.[209]

Other researchers argue that the effects of health and socioeconomic class are the primary cause of the gap. While they do not denny that racism may play a role they argue that efforts to close the gap should focus on factors related to health and economics.

Paul R. Sackett, Chaitra M. Hardison, and Michael J. Cullen write that the misinterpretation that removing threat from a testing setting eliminates all African American White differences may lead to the belief that there is less need for research and intervention aimed at a broad range of potential contributing factors, such as differences in educational and economic opportunities of African American and White youth.[210]

Possible explanations for how genetic differences could evolve

There are two mainstream[How to reference and link to summary or text] theories of the evolution of contemporary humans. The Recent single-origin hypothesis proposes that modern humans evolved in Africa and later replaced hominids in other parts of the world. The multiregional hypothesis proposes that modern humans evolved to some degree from independent hominid populations. An emerging synthesis theory proposes that the genes of contemporary human are predominantly descended from a recent African origin, but that interbreeding with other hominids may have contributed genes to local populations (Templeton 2002). Eswaran et al. (2005) speculate that "as much as 80% of the nuclear genome is significantly affected by assimilation from archaic humans (i.e., 80% of loci may have some archaic admixture, not that the human genome is 80% archaic)."

The Imperial examination system in China and similar systems in other East Asians nations have been proposed as an explanation for the higher average IQ, compared for example with the caste system in India which made if much more difficult for the intelligent but poor to gain SES. Celibacy for priests have been invoked as an explanation for claimed lower IQ in Catholic countries, although this also seems to be contradicted by the equal IQ in northern and southern Europe. The earlier mentioned comparative European IQ study reported that there was a larger variation in IQ scores in southern Europe. Possible explanations for the earlier mentioned difference for this include sample selection, larger environmental differences affecting IQ scores between urban and rural areas in southern Europe at the time of the test (1981), and/or that northern Europe became socially stratified later in history, causing less genetic variation in IQ.

Rushton has proposed a controversial theory in his book Race, Evolution and Behavior. He argues that r/K selection theory is applicable to humans and explains racial differences in intelligence, as well as claimed differences in many other traits. The theory has been severely criticized using various arguments.

Constant persecutions favoring a high IQ have been proposed[attribution needed] as an explanation for the higher average Ashkenazi IQ, but other persecuted groups like the Romani do not score highly on IQ tests. Another theory suggests that there was selective breeding for Talmudic scholarship, but this seems unlikely to have been important because there weren't very many professional rabbis. A selective force that only affects a tiny fraction of the population can never be strong enough to cause important evolutionary change in tens of generations. A more plausible, but difficult to evaluate without detailed demographic information, variant of this is that achievement in Talmudic scholarship had high status and that rich families therefore preferred to marry their daughters to males who excelled in this. Yet another explanation, according to a 2005 study,[211] the most likely, is that they mostly worked jobs in which increased IQ strongly favored economic success, in contrast with other populations, who were mostly peasant farmers. (See "Natural History of Ashkenazi Intelligence")

↑PBS Jencks Interview "If we change the names of the tests, they still measure the same thing but it wouldn't convey this idea that somehow you've gotten the potential of somebody when you measured their IQ. And I think that creates a big bias, because the people who do badly on the tests are labeled as people with low potential in many people's minds and they sometimes even believe that about themselves."

↑Jencks and Phillips 1998 "... we find it hard to see how anyone reading these studies with an open mind could conclude that innate ability played a large role in the black-white gap."

↑Aristotle: "Having spoken of the number of the citizens, we will proceed to speak of what should be their character. This is a subject which can be easily understood by any one who casts his eye on the more celebrated states of Hellas, and generally on the distribution of races in the habitable world. Those who live in a cold climate and in Europe are full of spirit, but wanting in intelligence and skill; and therefore they retain comparative freedom, but have no political organization, and are incapable of ruling over others. Whereas the natives of Asia are intelligent and inventive, but they are wanting in spirit, and therefore they are always in a state of subjection and slavery. But the Hellenic race, which is situated between them, is likewise intermediate in character, being high-spirited and also intelligent. Hence it continues free, and is the best-governed of any nation, and, if it could be formed into one state, would be able to rule the world." (Aristotle, Politics, ch. 7).
Cicero: "Do not obtain your slaves from Britain because they are so stupid and so utterly incapable of being taught that they are not fit to form a part of the household of Athens." Attributed to Cicero's Epistulae ad Atticum (Letters to Atticus), 68 BC-43 BC (latin text). Translation: Cicero 1918.
"Races north of the Pyrenees are of cold temperament and never reach maturity; they are of great stature and of a white colour. But they lack all sharpness of wit and penetration of intellect." Attributed to "Said of Toledo (a Moorish savant)" by Benedict 1999 (p.34), originally quoted in Hogben 1931.

↑Aristotle: "Having spoken of the number of the citizens, we will proceed to speak of what should be their character. This is a subject which can be easily understood by any one who casts his eye on the more celebrated states of Hellas, and generally on the distribution of races in the habitable world. Those who live in a cold climate and in Europe are full of spirit, but wanting in intelligence and skill; and therefore they retain comparative freedom, but have no political organization, and are incapable of ruling over others. Whereas the natives of Asia are intelligent and inventive, but they are wanting in spirit, and therefore they are always in a state of subjection and slavery. But the Hellenic race, which is situated between them, is likewise intermediate in character, being high-spirited and also intelligent. Hence it continues free, and is the best-governed of any nation, and, if it could be formed into one state, would be able to rule the world." (Aristotle, Politics, ch. 7).
Cicero: "Do not obtain your slaves from Britain because they are so stupid and so utterly incapable of being taught that they are not fit to form a part of the household of Athens." Attributed to Cicero's Epistulae ad Atticum (Letters to Atticus), 68 BC-43 BC (latin text). Translation: Cicero 1918.
"Races north of the Pyrenees are of cold temperament and never reach maturity; they are of great stature and of a white colour. But they lack all sharpness of wit and penetration of intellect." Attributed to "Said of Toledo (a moorish savant)" by Benedict 1999 (p.34), originally quoted in Hogben 1931.

↑for example, the children of wealthy, high IQ Black parents score lower than the children of poor, low IQ White parents (Jensen 1998b, p. 358); and for Black and White children with an IQ of 120, the siblings of the Black children average an IQ of 100 whereas the siblings of the White children average an IQ of 110; in comparison, for Black and White children with an IQ of 70, the siblings of the Black children average an IQ of 78 whereas the siblings of the White children average an IQ of 85 (Jensen 1973, pp. 107–119))

↑Dolan and Hamaker 2001 reanalyzed the data from several earlier studies and concluded that Spearman's hypothesis is not an "empirically established fact" (i.e., that Black-White IQ differences may be due to differences in common factors other than g) due to insufficient power in the data to choose between alternative models. "This leaves the validity of Spearman's hypothesis, considered a central justification for the genetic explanation, an unresolved question." However, they did confirm that the Black-White IQ gap is not due to measurement artifacts, and is instead due to some measured factor that varies both within and between groups.

↑Flynn write: "But this is simply an escape from hard thinking and hard research. Racism is not some magic force that operates without a chain of causality. Racism harms people because of its effects and when we list those effects, lack of confidence, low self-image, emasculation of the male, the welfare mother home, poverty, it seems absurd to claim that any one of them does not vary significantly within both black and white America."

↑Socioeconomic status modifies heritability of iq in young children Eric Turkheimer, Andreana Haley, Mary Waldron, Brian D'Onofrio, and
Irving I. Gottesman. "The models suggest that in impoverished families, 60% of the variance in IQ is accounted for by the shared environment, and the contribution of genes is close to zero; in affluent families, the result is almost exactly the reverse."

↑How similar are fluid cognition and general intelligence? A developmental neuroscience perspective on fluid cognition as an aspect of human cognitive ability, Behavioral and Brain Sciences (2006), 29: 109-125 Cambridge University Press, Clancy Blair. Multiple comments can be seen on Google Scholar.

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↑Shuey 1966 reported the average correlation between skin color and IQ among American blacks is .1; for comparison Parra 2004 reported the correlation between skin color and fraction of West-African ancestry is .4.

↑Rushton and Jensen 2005b argue that these studies are "peculiarly old, the mean year of publication being 1960" and "actually very weak and nondecisive, not having been replicated even once". Jensen 1998b, for example, points out that while the study of children born in post-WWII Germany finds no difference between white and interracial children, it does find a large difference in IQ between boys and girls, suggesting that sampling artifacts have affected the results.

↑ 159.0159.1159.2Fryer and Levitt 2006Testing for Racial Differences in the Mental Ability of Young Children "On tests of intelligence, Blacks systematically score worse than Whites, whereas Asians frequently outperform Whites. Some have argued that genetic differences across races account for the gap. Using a newly available nationally representative data set that includes a test of mental function for children aged eight to twelve months, we find only minor racial differences in test outcomes (0.06 standard deviation units in the raw data) between Blacks and Whites that disappear with the inclusion of a limited set of controls. The only statistically significant racial difference is that Asian children score slightly
worse than those of other races. To the extent that there are any genetically-driven racial differences in intelligence, these gaps must either emerge after the age of one, or operate along dimensions not captured by this early test of mental cognition."

↑Neil Risch argues: "One could make the same arguments about sex and age! . . you can undermine any definitional system. . . In a recent study. . . we actually had a higher discordance rate between self-reported sex and markers on the X chromosome [than] between genetic structure [based on microsatellite markers] versus [racial] self-description, [which had a] 99.9% concordance. . . So you could argue that sex is also a problematic category. And there are differences between sex and gender; self-identification may not be correlated with biology perfectly. And there is sexism. And you can talk about age the same way. A person's chronological age does not correspond perfectly with his biological age for a variety of reasons, both inherited and non-inherited. Perhaps just using someone's actual birth year is not a very good way of measuring age. Does that mean we should throw it out? . . . Any category you come up with is going to be imperfect, but that doesn't preclude you from using it or the fact that it has utility" (Gitschier 2005).

The technical errors contained in Rowe’s (2005) article include both misuse of broad scientific concepts and incorrect or biased misinterpretation of specific scientific data. The author’s broad argument assumes that a quantity definable as “intelligence” exists (in contradistinction to the view that multiple types of cognitive functioning can be identified that are valued and manifested differently, conditional on the setting and the observer), that intelligence can be measured with “IQ tests,” that demographic groups known as “continental races” divide humans into discrete categories on the basis of important concordant variation in genetically determined traits, that molecular genetics can (or will) make it possible to define the architecture of complex traits in terms of “genes for X or Y” (i.e., “genes for intelligence”), and that significant variation in polymorphisms in those genes overlap with the traditional demographic categories, such as those promulgated by the U.S. government.

References

The two most widely-known works concerning race and intelligence are The Mismeasure of Man by Stephen Jay Gould, originally published in 1981, and The Bell Curve by Richard Herrnstein and Charles Murray, published in 1994. Media controversy surrounding The Bell Curve motivated Gould to revise and expand The Mismeasure of Man to respond to arguments from The Bell Curve, publishing the book's second edition in 1996. Many current researchers think that both books are outdated due to new research.

External links

A recent review summarizing the arguments for a "partly-genetic" explanation can be found here:[7]